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Networking Fundamentals · Intermediate

Start of Authority Record (SOA)

The DNS record at the top of every zone that names the primary server, administrator email, serial number and timers.

Definition

The serial number must increase when the zone changes so secondaries know to transfer it. The SOA also sets refresh, retry, expire and negative-caching TTL values.

Example

example.com. SOA ns1.example.com. hostmaster.example.com. 2026110101 ...

Exam tip

Secondaries pull updates only when the SOA serial increases.

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